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LGS GCSE OCR Physics > P6.1 - Radioactive Emissions > Flashcards

P6.1 - Radioactive Emissions Flashcards

1
Q

What are isotopes?

A

Isotopes are atoms of the same element (same number of protons) containing a different number of neutrons.

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2
Q

Some isotopes of an element may be…?

A

Some isotopes of an element may be stable whilst others are unstable and decay, emitting alpha, beta or gamma radiation.

E.g. - Carbon-12 is completely stable whereas Carbon-14 is radioactive - Those extra 2 neutrons make the entire nucleus unstable. An unstable nucleus has too much energy and must get rid of it.

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3
Q

What does an unstable nucleus have to do?

A

An unstable nucleus has too much energy and must get rid of it.

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4
Q

What is nuclear radiation?

A

Nuclear radiation is just emitted energy by a nucleus of an unstable atom.

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5
Q

What are the properties of alpha radiation?

A
  • Particles.
  • A helium nucleus.
  • Stopped by a few sheets of
    paper/skin or cm of air.
  • Heavily ionising.
  • Slow.
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6
Q

What are the properties of beta radiation?

A
  • Particles.
  • Fast moving electron.
  • Stopped by a few mm of
    aluminium.
  • Moderately ionising.
  • Fast.
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7
Q

What are the properties of gamma radiation?

A
  • Wave.
  • High energy EM wave.
  • MOST is stopped by a few cm
    of lead or m of concrete.
  • Lightly ionising.
  • Speed of light
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8
Q

What is ionisation?

A

Ionisation is the process of turning a neutral atom / particle into an ion.

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9
Q

Why is nuclear radiation bad?

A
  • The three types of nuclear
    radiation are dangerous
    because they are ionising
    radiation.
  • Ions are extremely reactive.
- The system/ions are in a 
  higher energy state and 
  need to lose energy - 
  Incomplete outer shell so 
  they react with
  neighbouring particles.
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10
Q

Explain why nuclear radiation is so dangerous to the human body?

A
  • Nuclear radiation is ionising.
  • If the ions are created
    near/in the body, they will
    react with the cells of the
    body.
  • The cells become damaged.
  • The damaged cells continue
    to replicate as normal cells
    do, giving rise to a tumour.
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11
Q

Which type of nuclear radiation is the least and most dangerous outside the body?

A 
- Alpha radiation is the least 
  dangerous because it can't 
  penetrate the skin.
- You get skin cancer at worst 
  which you can just cut off.
- Gamma is the most dangerous 
  because it can penetrate the 
  skin 
- Although there is a lower 
  change of ionisation than 
  alpha radiation, any ions 
  created will damage cells of 
  vital organs.
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12
Q

Which type of nuclear radiation is the least and most dangerous inside the body?

A
  • Alpha radiation is the most
    dangerous because it is
    heavily ionising.
  • Gamma radiation is the
    least dangerous because it
    can penetrate the body and
    leave it.
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13
Q

Why does alpha radiation have a much smaller range than gamma radiation?

A
  • You have to transfer energy
    to an atom to ionise it.
- Alpha particles transfer 
  more energy to the material 
  they are travelling through 
  than gamma rays because 
  they are highly ionising.
  • Therefore alpha radiation has
    a much shorter range.
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14
Q

What does a heavier/unstable isotope mean?

A

Higher likelihood of it emitting all three types of radiation.

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15
Q

What happens when a beam of radiation is passed through an electric field between a positive and negative plate?

A

Alpha particles - Attracted towards the negatively charged plate because it has a positive charge.

Beta particles - Attracted towards positively charged plate because it has a negative charge - Deflection of beta is much greater owing to its much smaller mass.

Gamma radiation experiences no deflection because it has no charge.

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16
Q

What happens to the nucleus in alpha radiation and what is the equation?

A
  • The number of protons and
    neutrons decrease as the
    nucleus lose two protons
    and two neutrons.
  • Mass number decreases by
    4.
  • Proton number decreases by
    2 - New element.
17
Q

What happens to the nucleus in beta radiation and what is the equation?

A
  • A neutron decays to a
    proton and an electron
    which is emitted as a beta
    particle.
  • Proton number increases by 1. - New element.
18
Q

What happens to the nucleus in gamma radiation and what is the equation?

A
  • Nucleus emits a high
    frequency electromagnetic
    wave.
  • No change to mass number
    and atomic number.
19
Q

What happens to the nucleus in neutron emission and what is the equation?

A
  • Nucleus emits the neutron.
- Mass number decreases by 
  1
- Proton number stays the 
  same.
- Same element.
20
Q

What type of process is radioactive decay?

A
  • Radioactive decay is a
    random process.
  • You cannot predict when a
    single unstable nucleus will
    decay and emit nuclear
    radiation.
21
Q

What is half life?

A 
- The time taken for half the 
  unstable nuclei in a 
  radioactive substance to 
  decay.
- The time taken for the 
  activity to half.
22
Q

What is the activity?

A
  • The number of nuclei that
    decay every second.
  • The total number of
    emissions per second.
- Can be measured by a 
  Geiger counter - Each click is 
  a tiny current produced when 
  the radiation ionises atoms of 
  the gas inside the tube.
  • Units = becquerels (Bq).
23
Q

What is the position of electrons in an atom?

A
  • Electrons in atoms, don’t actually “orbit” around
    the nucleus.
  • Instead, electrons occupy (discrete) energy levels.
24
Q

Explain the idea of energy levels?

A
  • Different energy levels are at different
    distances from the nucleus.
  • The lowest energy level is closest to the nucleus.
  • Different atoms have different values for energy
    levels.
25
Q

What can happen to electrons in low energy levels and how?

A
  • Electrons in low energy levels, can move up to a
    higher energy level by gaining energy - the
    electrons are excited to higher energy levels.
  • The electrons in atoms can be excited by
    absorbing EM radiation.
26
Q

What does the EM radiation for the excitation of the electrons have to have?

A
  • Only incident EM radiation of an exact, certain
    frequency can excite electrons in a particular
    energy levels.
  • This is a very strange fact that cannot be
    explained by considering EM radiation to be a
    wave.
  • Instead, Physicists consider EM radiation to
    consist of “particles of light” known as photons.
27
Q

Explain how an electron excites.

A
  • A single photon is absorbed entirely by a single electron.
  • The energy of the photon is proportional by the frequency of the EM radiation.
  • If the energy of the photon exactly matches the
    difference in energy between the two levels, the
    electron will excite to a higher energy level.
28
Q

Why does an electron have to de-excite?

A
  • Only a certain number of electrons are allowed to
    exist at any given energy level.
  • Thus, electrons that have excited to higher energy
    levels, will de-excite and return to their original
    energy level.
29
Q

Explain how an electron that has excited more than one energy level de-excites.

A
  • An excited electron will de-excite and return to
    its original energy level and emit radiation.
  • The electron will de-excite in steps.
  • Each time it de-excites, it emits energy in the
    form of a photon of a given frequency.
  • The emitted photons are of lower energy (and
    therefore frequency and longer wavelengths) than the original photon
    that was absorbed and caused excitation.
30
Q

What is one way to excite electrons?

A

One way to excite electrons in the atoms of a gas is to pass electric current through it.

31
Q

What is an emission spectrum?

A

An emission spectrum shows a set of frequencies of radiation emitted by an atom when excited electrons move to lower energy levels.

32
Q

What does the frequency of radiation emitted when electrons de-excite depend on?

A

The frequency of radiation emitted depends on the difference in energy of the energy levels.

33
Q

What happens as UV photons excite electrons.

A

Lower frequency, visible light photons emitted as electrons de-excite.

34
Q

What is an absorption spectrum?

A

An absorption spectrum shows a set of frequencies of radiation absorbed by an atom when excited electrons move to higher energy levels.

35
Q

Give an example of how a star’s absorption spectra looks.

A
  • Light emitted from stars contain all frequencies of
    EM radiation.
  • As light passes through stars, certain frequencies of
    photons get absorbed by hydrogen and helium
    atoms.
  • The frequencies that match in energy to the energy
    difference between the energy levels appear as
    black lines in the star’s spectra.
36
Q

Describe the difference between an ‘excited’ atom and an ‘ionised’ atom?

A
  • In an excited atom, orbital electrons are in a higher
    energy state/level.
  • In an ionised atom, orbital electrons have left the
    energy levels of the atom.
37
Q

Describe in terms of the electrons what happens when:
A) Photons are absorbed
B) Photons are emitted

A

A) Electrons excite to a higher energy level.

B) Electrons de-excite to a lower energy level.

38
Q

Suggest and explain why hydrogen cannot emit X-ray photons.

A
  • The energy of emitted photons is equivalent to the
    energy difference between energy levels in an atom.
  • Hydrogen energy levels must not have a difference
    large enough to give rise to high energy X-ray
    photons.
39
Q

Explain why some atoms can absorb ultraviolet radiation, but emit visible light (and so glow in the dark).

A
  • Some atoms absorb UV radiation, as there exists
    an energy difference between their energy level,
    that exactly matches the energy of the UV
    photons.
  • After absorbing a UV photon, an orbital electron
    will excite to a higher energy level.
  • The excited electron will then de-excite to its
    original energy level, in steps, emitting photons of
    energy equivalent to the energy different between
    the levels.
  • The energy difference between the levels
    matches the energy of visible light photons.

LGS GCSE OCR Physics (23 decks)

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